glsl: Don't emit ir_binop_carry during ir_binop_imul_high lowering

glsl: Don't emit ir_binop_carry during ir_binop_imul_high lowering

st_glsl_to_tgsi only calls lower_instructions once (instead of in a
loop), so the ir_binop_carry generated would not get lowered.  Fixes
assertion failure

state_tracker/st_glsl_to_tgsi.cpp:2265: void glsl_to_tgsi_visitor::visit_expression(ir_expression*, st_src_reg*): Assertion `!"Invalid ir opcode in glsl_to_tgsi_visitor::visit()"' failed.

on softpipe in 16 piglit tests:

    mesa_shader_integer_functions/execution/built-in-functions/fs-imulExtended-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-imulExtended-only-msb-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-imulExtended-only-msb.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-imulExtended.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-umulExtended-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-umulExtended-only-msb-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-umulExtended-only-msb.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/fs-umulExtended.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-imulExtended-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-imulExtended-only-msb-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-imulExtended-only-msb.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-imulExtended.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-umulExtended-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-umulExtended-only-msb-nonuniform.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-umulExtended-only-msb.shader_test
    mesa_shader_integer_functions/execution/built-in-functions/vs-umulExtended.shader_test

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>